Testing positive, then what?

It's a good question (one for which I do not know the answer), because Positive PCR tests can also remain positive days and weeks after an infection. In our lab, we report them as "low Level Positives" based on the estimated viral load (which in turn is calculated on the number of replication cycles the test requires to flag positive. In general, a real positive will be between 12-25 cycles on our systems, whereas "residue" positives will often be in the range >35 cycles)

As far as I know, you can’t leave isolation until you test negative. In the summer, some British lads were stuck abroad for more than 3 months as they were still testing positive weeks after the symptoms disappeared.

I think you have to have a letter from a physician that you have recovered. Symptom free for X number of days. Each country may have different rules.

Here is how it is handled by the CDC for returning to the States and my personal experience testing positive in France. I had to isolate for ten days, and then I needed a doctor's letter to be able to board the plane to the States on day 11 or afterwards because, indeed, a person can test positive after recovering. In fact, as you can read in the link to the CDC within this account, the CDC states not to retest, as did the French health service.

An isolation period of ten days is the same in Germany; you would need to confirm on an official National Health Service website the required isolation length in England. Everything else is speculation. And with the more contagious variant, rules could change, but probably not before you fly. This happened to me a month ago. Here are the steps to prove you are safe to board a plane:

https://community.ricksteves.com/travel-forum/covid19/positive-test-flying-to-the-states-what-do-you-do-personal-experience

PS another shout out to Pam on this website who sent me all this information when I tested positive.